Abstract: In order to achieve high-resolution pictures of the ground, it is necessary to achieve high resolution along the radar beam (range resolution), and across the beam (cross-range resolution). High range resolution is achieved by the use of pulse compression. Cross-range resolution is a function of antenna beamwidth and target range. High cross-range resolution, therefore, is achieved by producing a radar antenna with a very narrow effective beamwidth. To achieve this, a real antenna would have to be made impracticably large. The solution is to find some way of synthesising the performance of a very large antenna out of one that is physically far smaller. This review article outlines the principles behind Synthetic Aperture Radar, and discusses the processing techniques used in the production of the final imagery. The technique of Inverse SAR (ISAR) is also briefly discussed.